Method of lead coating ferrous alloys containing a. relatively high percentage of chromium



Patented May 23, 1933 L. SA'I'IEB, OF TAREN'I'UI, PENNSYLVANIA,

ASBIGNOR TO ALLEGHENY STEEL COMPANY, 01 BRAGKENBIDGE, PENNSYLVANIA, A. CORPORATION OF ramm- .VAN'IA.

METHOD 0] LEAD COATING IEBROUS ALLOYS CONTAINING A. RELATIVELY HIGH PERCENTAGE OF OHIBDHIU]! No Drawing.

This invention relates to the lead coating of articles made from ferrous alloys and particularly to articles made from alloys having an appreciablechromium content.

Included within these alloys are those known as stainless steel and rustless iron as well as those alloys containing appreciable amounts of chromium and nickel with or without other metals or metalloids.

While it is common to coat ironand steel articles with lead and other lubricating metals no one so far as I know, has been able before this invention to coat with lead ferrous alloys having an appreciablechromium content.

The lead coating of articles made from such alloys is done with the object in view of facilitating further reduction or finishing, by drawing, stamping, rolling or otherwise cold working.

The methods commonly, practiced commercially for the coating of iron and steel articles have been fairly satisfacto in in coating iron or steel articles, but I ave found that none of the methods with which I am familiar is satisfactory where the article 'to be coated is madefrom a ferrous alloy having an appreciable chromium content.

An object of this invention is to provide a method whereby articles made from fer-.- rous alloys containing appreciable amounts of chromium can be readily coated with a soft metal such as lead.

A further object is to provide a method by means of which articles made from ferrous alloys containing from about 6% to about chromium and from alloys containing from about 6% to about 30% chromium with from about 20 to about nickel can be readily coated with dense, adherent lead suitable as a lubricant for facilitating further work such as drawing, stamping, rolling, etc.

A urther object of this invention is to Application fled February 28, 1828. Serial No. 842,952.

produce lead coated articles made from ferrous alloys having a chromium content in excess of 8%.

A still further object is to provide a method by means of which tube blanks and wire blanks made from a fcrrous'alloy containing in excess of 6% chromium may be readily cold drawn into finished products.

In carrying out this invention, I prepare a bath of molten lead of the proper size as.

to length, breadth and depth to accommodate the articles to be coated. The bath container and the apparatus for maintaining the bath at the desired temperature can be of standard design.

I find that it is preferable to maintain the bath at a working temperature of about 100 F. above the melting oint of lead in order to offset the cooling e ect of the articles being coated. This temperature will give heavier lead coats than higher temperatures, therefore, if thinner coats are desired, the temperature should be raised.

Upon the molten lead bath I place zinc chloride and ammonium chloride in suflicient amounts to. form when melted, a relatively thin layer of molten flux. It is preferable, as will later appear, to keep the am.- monium chloride content between 1.5%

Upon the bath made up of molten lead with the superim sed combined fluxes of zinc chloride an ammonium chloride, I preferably sprinkle a small amount of sawdust. Oxidation of the lead is inhibited by the superim osed layer of molten zinc and ammonium chlorides aided by the sprinkling of sawdust. A mild stirring of the fluxes shows that the oxides are eifectively reduced and that a very clean molten lead is obtained.

The articles to be lead coated are first pickled to remove thescale and it is preferable to rinse the. articles after they are pickled and to dry the same, before they are treated in the bath.

and 2%.

I have found that while articles made from the alloys in uestion cannot be satisfactoril lead coate by immersing the same in the ath prepared in the above manner, the can be given a dense, adherent coating of ead by means of such bath, if they are so manipulated that the surfaces to be coated are caused to contact alternately with the double chloride flux and the molten lead when the articles have reached the temperature of the molten lead.

In coating tube or pipe blanks, the blanks which float on the molten lead are rotated or spun. The layer of double chloride flux is preferably kept so shallow that a blank floating on the lead bath will only be partially submerged in the flux and will project into the atmosphere immediately above the flux.

Ammonium chloride alone begins to separate into ammonia gas and hydrochloric acid gas at about 350 F., the ratio of the gases remaining molecularly constant. These two gases upon condensing together again form ammonium chloride. In the molten state, zinc chloride and ammonium chloride form double salts which are stable below 500 F. and slightly unstable at the melting point of lead. At 1000 F. the double salt is uite unstable.

inc chloride in the hygroscopic state hegins to melt at-about 250 F. while lead melts at about 621 F.

Zinc chloride in the anhydrous state has a melting point of about 690 F. Hygroscopic zinc chloride can be heated to 690 F. with a quiet bubbling evaporation of the water content. The water content at 690 F. or higher may exist for from 5 to 10 minutes. After evaporation of the water content, it may be heated up to 1000 F. with slight volatilization at the higher temperatures.

Evidently, the rotating or spinning of the tube blanks on the surface of the lead bath with the blanks rejecting above the double chloride flux su jects the surface of the blanks to the escapin hot ammonium chloride gas at the sur ace of the molten double salts. Air moisture contact on. the surface also probably takes place and it is my belief that both the escaping hot ammonium chloride gas and the moist air contact assist in causing the molten lead to adhere to the surfaces of the articles being coated.

If wire is to be coated, it is preferably first coiled, then pickled, rinsed and dried and then slowly rotated with the axis of the coil horizontal or nearly so, so that the surfaces of the wire are alternately subjected to the hot gases above the fluxsurface, the flux and the molten lead. If sheets or plates areto be coated, they arepreferably-dmped the desired number of times either on edge parently or flat, so that the surfaces thereof contact alternately with the hot gases, the molten flux and the molten lead. Suflicicnt time necessary to bring the articles to the proper temperature is required.

'My experience indicatcsthat the alloys in question will not lead coat unless the zinc chloride double salt contains at least 1.5% ammonium chloride at the operating temperature.

Below this percentage there will be little or nolead coating. Above this concentration of ammonium chloride the reaction appears to be about the same. There .secllis to be no advantage in maintaining the ammonium chloride concentration above 2% since the loss of ammonium chloride from the double salt at operating temperature appears to be as follows 10% ammonium chloride in zinc chloride loses 2% ammonium chloride per hour. while 1.0% ammonium chloride in zinc chloriilc loses but 1% per hour. It would appear that an amount of ammonium chloride in cxcess of 2% is uneconomical and is of no advantage 'as the lower percentages of :innnoniun1 chloride content are much more stable al operating temperatures than when an excess is present.

lVhile I have bccn unable to find any substitutes for the zinc chloride, I have found that the salts of aluminum chloride. ammonium phosphate, stannous chloride or stannous sulphate can be used for lead coating the alloys in question in combination with zinc chloride and instead of ammonium chloride.

The use of either aluminum chloride, ammonium phosphate, stannous chloride or stannous sulphate as a substitute for ammonium chloride does not appear practical for two reasons. In the first place, ammonium chloride is cheaper than any of these other substitutes and second, and of greater importance, is that the use of aluminum chloride over a period of time causes an interference from its non-volatile decomposition product aluminum oxide. The tin saltsshow an accumulation of non-volatile metallic tin which has a tendency to alloy with the lead. Ammonium is the best substitute for mumonium chloride, but the volatile )hosphoric products which are driven o are dangerous on account of their toxic prop- A of their removal by erties and the difliculty ventilation.

Ammonium sulphate and the alkaline earth chlorides and sulphates as well as the remainder of the metal chlorides and sulphates are without effect when used in place of ammonium chloride and with anhydrous zinc chloride. The latter chlorides as a substitute for ammonium chloride do show a tendency to'lead coat when dissolved in the phosphate apmolten zinc chloride if all of the water has not been driven out of the zinc chlorlde. This condition, however, cannot be mamtained when operating commercially.

I am lead to believe that the use of ammonium chloride is preferable to any of the substitutes, because its decomposition products as well as the salt itself are volatile and non-toxic and while the vapors iven oil therefrom are irritants, they can safely removed by proper ventilation.

What I claim as new and desire to secure by Letters Patent is:

1. The method of lead coating a tube blank made from a chromium-containin ferrous alloy, which consists in floating suc blank upon a molten bath of lead having a molten flux supported thereon, said blank projecting above said flux and in rotating or s inning the blank so that the surfaces t ereof alternately contact with the flux and the molten lead bath.

2. A method of the character disclosed comprising preparing a'bath of molten lead, placing enough zinc and ammonium chlorides on said bath to form a relatively thin layer of molten flux, and rotating chromiumcontaining articles floatin on the lead bath and projecting through t e flux thereon so that the surfaces thereof to be coated are contacted alternately with the flux and bath.

3. A method of the character disclosed comprising preparing abath of molten lead, placing enough zinc and ammonium chlorides on said bath to form a relatively thin layer of molten flux, and turnin chromiumcontaining articles floating on t e lead bath and projecting above the flux. thereon so that the surfaces thereof to be coated are contacted alternately with the flux and bath, and regulating the thickness of the coating by controlling the temperature of the bath.

4. A method of .the character disclosed comprising preparing a bath of molten lead, placing enough zinc and ammonium chlorides on said bath to form a relatively thin layer of molten flux, and spinning chromium-containing articles floating on the lead bath and projecting above the flux thereon so that the surfaces thereof to be coated are contacted alternately with the flux and bath, 1 and regulating the thickness of the coating by controlling the temperature of the bath, the higher the temperature the thinner being the resulting coating.

5. A method of the character disclosed comprising preparing a bath of molten lead, placing enough zinc and ammonium chlorides on said bath to form a relatively thin layer-of molten flux, and rotating chromium-containin articles floatin on the lead bathLand prqectin through t 1e flux thereon so that the surfices thereof to be coated are contacted alternately with the flux and contacted alternately bath, and sprinkling sawdust on said molten flux prior to immersion of said articles.

6. A method of the character disclosed comprising preparing a bath of molten lead, placing enou h zinc and ammonium chlorides on said ath to form a relatively thin layer of molten flux,,and rotating chromium-containing articles floating on the bath and projecting through said flux so that the surfaces thereof to be coated are contacted alternatel with the flux and bath, said ammonium c loride being kept within the limits of 1.5-2%

7. A method of the character disclosed comprising preparing a bath of molten lead, placing enou h zinc and ammonium chlorides on saiddiath to form a relatively thin layer of molten flux and turning chromiumcontaining articles floating on said bath and projecting through said flux so that the suraces thereof to be coated are contacted alternately with the flux and bath, said ammonium chloride being maintained at a constant value between 1.5% and 2%.

8. A method of the character disclosed comprising preparing a bath of molten lead, placing enough zinc and ammonium chlorides on said bath to form a relatively thin layer of molten flux, and rotating chromium-containing articles floating on said bath so that the surfaces thereof to be coated are contacted alternately with the flux and bath said articles being pickled, rinsed and dried prior to immersion 9. A method of the character disclosed comprising preparing a bath of molten lead, placmg enough zinc and ammonium chlorides on said bath to form a relatively thin layer of molten flux, and rotating chromiumcontalning articles floating on said bath so that the surfaces thereof to be coated are. contacted alternately with the flux and bath, said articles containlng said chromium within the limits of about 630%.

10. method of the character disclosed comprising preparing a bath of molten lead, placing enough zinc and ammonium chlorides on said bath to form a relatively thin layer of molten flux, and rotating chromiumcontaining articles floating on said bath so that the'surfaoes thereof to be coated are with the flux and bath, sald articles containing at least about 8% chromium.

11. method of the character disclosed comprising preparing a bath of molten lead, placing enough zinc and ammonium chlorides on said bath to form a relatively thin layer of molten flux, and rotating chromiumcontaining tube blanks floating on said bath and of a diameter greater than the depth of the flax so that the surfaces thereof to be coated are contacted alternately with the flux and bath," and then in cold drawing said tube blank to form a finished tube.

12. The method of, lead coating chromium allo articles comprising forming a molten lea bath with a su rnatant double chloride flux, artially su mergi the alloy articles to be coated in said ath and flux until they attain the temperature of the bath, and then rotating such articles so that the surfaces thereof alternately contact with the double chloride flux and the molten lead until the desired coating is formed.

13. The method of lead coating chromium alloy tube blanks comprising forming a. molten lead bath with a suitable supernatant relatively shallow flux, floating the tube blanks ufign the bath in such a position that the blan are partially submerged in the bath and flux and have portions projecting into the atmosphere above the flux until the blanks have attained the temperature of the bath, and then rotating the blanks to contact the surfaces thereof alternatel with the flux and molten lead until the desired coating is formed.

In testimony whereof, I have hereunto subscribed my name this 21st day of February, 1929.

LOUIS L. SATLER.

CERTIFICATE OF CORRECTION.

Patent No. 1,910, 366. May 23, 1933.

LOUIS L. SATLER.

it is hereby certified that error appears in the printed specification oi the above numbered patent requiring correction as follows: Page 3, line 10, after "safely" insert the words "and easily"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this lst day of August, A. D. [933.

M. J. Moore.

(Seal) Acting Commissioner of Patents.

12. The method of, lead coating chromium allo articles comprising forming a molten lea bath with a su rnatant double chloride flux, artially su mergi the alloy articles to be coated in said ath and flux until they attain the temperature of the bath, and then rotating such articles so that the surfaces thereof alternately contact with the double chloride flux and the molten lead until the desired coating is formed.

13. The method of lead coating chromium alloy tube blanks comprising forming a. molten lead bath with a suitable supernatant relatively shallow flux, floating the tube blanks ufign the bath in such a position that the blan are partially submerged in the bath and flux and have portions projecting into the atmosphere above the flux until the blanks have attained the temperature of the bath, and then rotating the blanks to contact the surfaces thereof alternatel with the flux and molten lead until the desired coating is formed.

In testimony whereof, I have hereunto subscribed my name this 21st day of February, 1929.

LOUIS L. SATLER.

CERTIFICATE OF CORRECTION.

Patent No. 1,910, 366. May 23, 1933.

LOUIS L. SATLER.

it is hereby certified that error appears in the printed specification oi the above numbered patent requiring correction as follows: Page 3, line 10, after "safely" insert the words "and easily"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this lst day of August, A. D. [933.

M. J. Moore.

(Seal) Acting Commissioner of Patents. 

